A. Technical Field
The present invention relates to an open-ended filter screen mounted in the spray boom supply line of the on-off control valve assembly of aircraft crop dusting spraying systems at the opening of the drilled passage which connects the low pressure area of the suck back Venturi to the spray boom supply line.
B. Description of Prior Art
The unwanted discharge of pesticides and other chemicals used during crop dusting is a serious concern. Aircraft operators and landowners who spill crop dusting materials onto the property of others or into surface waters face substantial liability under state tort law as well as federal environmental law. For example, some state and federal environmental laws impose liability for pollution and personal injury even if an operator or land owner is completely free of fault. Thus, there is a great need for crop dusting systems which minimize such unwanted discharges.
An aircraft liquid crop spraying system is composed of several different parts. The liquid which will be sprayed is stored in an internal hopper or tank. The spraying equipment often consists of an assembly bolted to the bottom of the hopper tank that supports a pump 2 and an on-off control valve 9.
The liquid to be sprayed is forced from the hopper into the on-off control valve 9 via a pump 2. When the on-off control valve 9 is open (FIG. 1), the liquid passes through the valve 9 into a large strainer prior to entering the spray boom. The spray boom is customarily attached to the trailing edge of the wing by hangers fastened to the wing's frame. Nozzles for atomizing the spray are placed along the boom on each wing. Each nozzle has a spring loaded, diaphragm cutoff valve. The pump pressure forces the diaphragm valves open, and the liquid is sprayed through the nozzles.
When the on-off control valve 9 is in the closed position (FIGS. 2 & 8), crop dusting fluids are recirculated 14 back to the hopper for agitation. The recirculating fluid passes through a suck back Venturi 7 located in the on-off control valve 9. The low pressure area of the Venturi 6 is connected to the spray boom supply line 10 via a small drilled passage 1. The drilled passage 1 allows fluid to be drawn from the boom into the low pressure area 6 of the Venturi 7 during recirculation (FIG. 2).
Drawing fluid from the boom through the drilled passage 1 effectively lowers the boom pressure and enables the diaphragm valves on the spray nozzles to close quickly. In other words, the quicker the boom fluid pressure drops, the quicker the spray nozzles close, thereby preventing waste and environmental contamination caused by unwanted fluid discharges during turns and ferrying.
Keeping the drilled passage 1 free of obstructions is critical to preventing unwanted liquid loss. However, pesticides and other spraying fluids often contain foreign particles such as rubber, glass, gravel or dirt. As the fluid is being drawn from the spray boom through the drilled passage 1 in the recirculating mode (FIG. 2), the foreign particles present in the fluid often obstruct or block the drilled passage 1. This blockage in the drilled passage 1 impedes the drop in boom pressure, causing the nozzles to drip during turns or while ferrying.
Blockage in the drilled passage 1 can also combine with other problems to cause unwanted fluid discharges. For instance, the on-off control valves 9 used in the industry typically employ a ball type valve 15. The placement of the ball in the valve determines whether the fluid used enters the spray boom or recirculates to the hopper for agitation after passing through the suck back Venturi 7. Through extended use, however, the ball and its corresponding seal often deteriorate and fail to provide a leak proof seal. Thus, fluid enters the spray boom while the system is in recirculating mode.
When the drilled passage 1 is clear, this fluid returns to the hopper via the drilled passage 1 due to the low pressure area 6 created by the suck back Venturi 7. When the drilled passage 1 is blocked, however, this fluid accumulates in the spray boom. Eventually, the boom pressure reaches a level sufficient to open the diaphragm valves causing unwanted discharge.
For the foregoing reasons, there is a need for an inexpensive device which prevents particles in crop dusting fluids from blocking the drilled passage 1 and causing unwanted and possibly unlawful discharges into the environment. The invention resolves the above problems by ensuring that the drilled passage 1 remains clear of debris. As will be shown below, its chief features, which can be embodied in a number of forms, allow filtered fluids 360 degree access to the drilled passage. Moreover, the inventions' self-cleaning feature, which occurs during the spray mode, ensures continuous access to both the drilled passage 1 and the spray boom.